I assme your question relates to residential properties. Durham Region runs significantly higher than other areas in the GTA.
A few tax rates, for residential properties, expressed as a percentage of the assessed value, in ascending order:
Toronto: 0.8308587%
Milton (urban part): 0.900159%
Mississauga: 0.972379%
Vaughan: 0.981623%
Richmond Hill: 0.986331%
Oakville: 0.986562%
Markham: 0.988053%
King: 1.034321%
Brampton: 1.145327%
Pickering: 1.293052%
Ajax: 1.324024%
Whitby: 1.326721%
Clarington: 1.333744%
Oshawa: 1.652185%
Toronto is the lowest in the GTA. Milton has low rates partly because they benefit from "slots" at Mohawk Raceway.
A comment: As has been discussed here once or twice previously, Toronto has kept residential tax rates low for many years by maintaining the highest rates, by far, on industrial and commercial properties. Miller pledged three years ago to phase in a correction to this situation, over a 15-year period, and residential rates in Toronto are therefore rising at a faster rate than for other municipalities. Some have (rightly or wrongly) blamed the current disparity for a flight of industrial and commercial development out of Toronto.
I won't set out a long list of tax rates for commercial properties. Suffice to say that Toronto (4.0634348% of assessed value) is a full percentage point higher than the next highest rates in the GTA (Clarington at 3.038680% and Ajax at 3.024587%).
The discrepancies aren't as large for industrial properties, but Toronto's tax rate for these is still above every other municipality in the GTA.